MOS power transistors or MOS power devices which are commonly employed in automotive and industrial electronics, should have a low switch-on resistance (Ron), when being switched on. In a switch-off state, they should have a high breakdown voltage characteristic and withstand source-drain voltages. For example, a MOS power transistor should withstand a drain to source voltage Vds of some tens to some hundreds volts when being switched off. As a further example, MOS power transistors conduct a very large current which may be up to some hundreds of amperes at a gate-source voltage of about 2 to 20 V at a low voltage drop Vds.
According to commonly employed technologies, lateral MOS transistors are used, which comprise a drain extension region or which are based on the so-called resurf concept. According to the resurf concept, in an off-state charges are removed by a doped portion which is disposed beneath the drift region. Alternatively, this doped portion may be implemented as an electrode disposed over the drift region and being insulated from the drift region. In order to further reduce the Rdson and the parasitic capacitances, new concepts for implementing a transistor are being searched for.